368 THE CANADIAN NATURALIST. [Oct. 



ON THE GEOLOGY OF EASTERN NEW YOKK. 



By Professor James Hall and Sir William E. Logan. 



Professor James Hall and Sir William Logan spent a few days 

 together last summer in examining some points of the geology of 

 Eastern New York, and propose to continue their examinations 

 next season, when we may expect from them a detailed account of 

 their results. Their principal object was to compare the rocks of 

 that region with some of those of Eastern Canada ; and I have 

 now permission, in the absence of these gentlemen, to lay before 

 this Society some of the results of this exploration. 



The shales of the Hudson River group, which are seen for a 

 considerable distance north and south of Albany, disappear a few 

 miles east of the Hudson, and are succeeded by harder and 

 coarser shales, sometimes red or green in color, and passing into 

 green argillaceous sandstones. These various strata, which are 

 associated with concretionary and shaly limestones, are now recog- 

 nized as belonging to the Quebec group. The line of contact 

 between this and the much more recent Hudson River group has 

 nowhere been clearly seen in this region, but the two series are 

 readily distinguished by their differences in color, texture, and 

 hardness, — differences which were formerly supposed to depend 

 upon the partial metaraorphism of the eastern portion, when this 

 was looked upon as a part of the Hudson River group. The 

 green sandstones and conglomerates of Grafton Mountain, formerly 

 looked upon as a portion of the Shawangunk conglomerate, are 

 recognized as belonging to an outlying portion of the Sillery for- 

 mation. This mountain Professor Hall had found in a previous 

 exploration (1844-45) to have, at a point farther south, a synclinal 

 structure, and it probably lies in three low synclinal axes. The 

 Sillery formation scarcely extends south of Rensselaer County. 



Canaan Mountain is also apparently synclinal, and, while lime- 

 stones appear in the valleys on each side of it, consists chiefly of 

 slates, the highest beds being a hard green sandstone, sometimes 

 shaly, without any of the conglomerates of the Sillery ; although 

 boulders and angular fragments of these are found in the adjacent 

 valleys. To the east of this, Richmond Mountain, in Massachu- 

 setts, presents in its upper portion a compact green slate, passing 

 upwards into a harder rock similar to that of the summit of Ca- 

 naan Mountain. To the southward, as far as Hillsdale, the 



